The present invention relates to a humidity detecting circuit with a humidity sensor for detecting the completion of the heating of an object and more specifically to a heating apparatus such as a microwave oven having a humidity sensor for detecting the completion of the heating of an food.
The conventional microwave oven uses two self-heated thermistors as a humidity sensor, the one being sealed in a dry atmosphere with 0 g/m.sup.3 absolute humidity, and the other being exposed to the exhaust gas discharged from the heating furnance. The humidity sensor of this type involves two thermistors as a pair that have virtually the same temperature coefficient and the same resistance at a high temperature. Besides, it is required to seal one of the pair in a dry atmosphere, causing high production cost.